The 9 piece set of spacers from Bluefire is a popular M54 accessory set we feel is a must have for any astro imager.  This shim set allows you to fine tune your spacing so you can dial in backfocus.

• Set of 9 aluminum spacer rings.
• Use to fine tune the spacing or introduce a small amount of rotation between M54 threaded accessories in an imaging train
• Includes 1 ring each of 0.1, 0.15, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8 and 1mm thicknesses
• Each ring is individually stamped with its thickness
• It is not uncommon for these to have minor scratches/scuffs/brown stains that look like rust but aren't. Functionality is not affected in any way.
• Please note that these spacer rings are unthreaded
• Nominal inside diameter = 54.1mm; nominal outside diameter = 62.1mm